The present invention is directed to a process for making a number of mineral, food or pharmaceutical grade salt products. The process is most preferably designed to achieve complete or nearly complete reaction of all reactants, resulting in high yield and purity in a shortened processing time to arrive at the desired final product having the sought after moisture content. Typically, a variety of salts are thus mass produced with reduced processing time and cost.
Unduly lengthy batch processes have been utilized to form a variety of mineral, food or pharmaceutical grade salt products such as calcium citrate, calcium malate, zinc citrate, magnesium citrate, and the like. Previously used processes for making the aforementioned products involve various steps. These steps, in general, are as follows: (1) mixing the reactants, sometimes with water, at ambient temperature (typically, about 25xc2x0 C. at 1 atmosphere pressure); (2) adding water to the mixed reactants, if not done in (1) above, at ambient temperature; (3) mixing the ingredients sometimes with heating to initiate reaction of the reactants; (4) after reaction has taken place, removing the so-heated product including any unreacted reactants from the reactor vessel; and (5) drying the product to the desired moisture content outside the reactor vessel.
Additionally, the previously used processes required extended drying times, typically outside the reactor vessel for achieving the desired moisture content within the mineral, food or pharmaceutical grade salt product. For example, using previously used processes to form the desired mineral, food or pharmaceutical grade salt product having the desired moisture content (typically from about 2% to about 6% moisture content) required a too long drying cycle, sometimes on the order of 1-5 days for product batches on the order of about 100 kg in size. Without being bound by theory, Applicants now believe that the long drying times are due to the addition of water in an amount thought to be necessary with the prior processes. Further, oftentimes the water and associated moisture content cause the formation of xe2x80x9clarge cakes.xe2x80x9d These xe2x80x9ccakesxe2x80x9d are required to be broken down and/or ground to manageable size granules to facilitate drying and to facilitate forming salt products having the desired moisture content. As a result, unfortunately, the overall cost, time, and process complexity for forming the desired salt products are disadvantageously increased.
Previously, the salt products were made in several steps, including conducting most of the drying of the salt products outside the reactor vessel, to accommodate the lengthier drying times. The disadvantages of having long drying times include, but are not limited to, requiring separate drying chambers or (in some cases) drying rooms, accommodating longer production times, and increasing costs of production. As a result, with prior processes, increased storage, processing space and processing time had to be allocated.
All of these factors contribute to increased production costs and decreased flexibility of using the processing equipment for switching from one salt product to another. Thus, for example, if one wanted to switch the product line from zinc citrate to calcium citrate, the longer processing times would delay the switch over because the drying chambers would be occupied with as yet undried product. One had to wait until the product was sufficiently dried before the drying chamber could be vacated for drying the next product in the same chamber. Alternatively, a separate drying chamber was needed if both products were to be dried simultaneously. The cost of such measures can be nearly or altogether eliminated using the presently claimed inventive process which utilizes less water than previously thought necessary.
Until now, for comparable batch sizes (e.g., about 100 kg batches) nearly complete reaction of the starting reactants with the desired purity and yield was not achieved while obtaining the desired shortened processing time goals, typically on the order of from about 1 to about 9 hours, preferably from about 1 to about 6 hours, more preferably from about 1 to about 2 hours, even more preferably about 1 hour, and most preferably about xc2xd-1 hour or less. The desired purity level of mineral, food or pharmaceutical grade salt products is that which is suitable for the intended use of the same, e.g. as a mineral, as a food ingredient, or as a pharmaceutical ingredient. For mineral, food or pharmaceutical grade salt products, the desired purity will often be that specified in the United States Pharmacopeia, 21st Edition, 1985 (or its later editions), in Remington""s Pharmaceutical Sciences, 16th Edition, Mack Publishing Co., Easton, Pa., 1980 (or its later editions), or in the Handbook of Chemistry and Physics, 57th Edition, CRC Press, Cleveland, Ohio, 1977 (or its later editions). For food grade salt products, the purity level may often be lower than that specified for pharmaceutical grade salt products.
The desired yield (actual/theoreticalxc3x97100=% yield) for mineral, food or pharmaceutical grade salt products is on the order of from about 90% to about 100%, preferably from about 95% to about 100%, more preferably from about 96% to about 100% and most preferably from about 98% to about 100% or 98%-100%.
It is desirable to provide a process for making mineral, food or pharmaceutical grade salt products in a single reactor vessel (including completing or nearly completing the drying step) wherein the yield and purity are high and the processing time is substantially shortened. It also is desirable to provide a process wherein the drying step of the process is short enough that it can be completed in the reactor vessel itself (preferably, from the start of the processxe2x80x94mixing the dry reactantsxe2x80x94to its finishxe2x80x94forming the desired product to at least the desired product moisture content and optionally meeting any other product specifications) in a relatively short processing time (e.g., preferably, on the order of 1-6 hours, more preferably 1-2 hours, even more preferably 1 hour, and most preferably xc2xd-1 hour or less as opposed to 1-5 days for comparable batch sizes from about 50 kg to about 600 kg) without having to resort to the use of a separate drying chamber.
It also is desirable to provide a process for making mineral, food or pharmaceutical grade salt products in a single reactor vessel wherein the yield is on the order of 95-100%, the purity level satisfies the product specification, the processing time is on the order of about 1-2 hours and the drying, sufficient to satisfy the product specification (e.g., about 6% by weight or less moisture content), also can be completed in the reactor vessel itself within the 1-2 hours processing time. Alternatively, it is desirable to provide the aforementioned process except that the drying is conducted in a drying vessel or drying chamber other than reactor vessel itself; however, the total processing time including the drying time is still completed within the 1-2 hours processing time for a 20-600 kg (e.g., 50 kg, 100 kg or 150 kg batch) batch of dry or essentially dry necessary reactants. Necessary reactants are those required to form the desired product.
It is thus an object of the present invention to provide a process for making mineral, food or pharmaceutical grade salt products wherein a high purity level and yield are achieved and the final product is formed with the desired moisture content (e.g. by completing or substantially completing the drying in the reactor vessel itself) in a substantially shortened processing time for comparable yields and purity over those achieved with prior processes. It is desirable to provide such a process for the cost savings and for the other associated advantages which will be readily apparent to one of ordinary skill based on the disclosure of this patent application.
It is yet another object of the present invention to provide the aforementioned process to reduce the processing time for example, from about 1-5 days down to preferably about 1-6 hours, more preferably about 1-2 hours, even more preferably about 1 hour, and most preferably about xc2xd-1 hour or less, and thereby reduce the costs and inconveniences associated with such process (for comparable batch sizes such as 100 kg, with comparable or better yield and purity).
These and other advantages are achieved by the inventive process noted below. According to one embodiment of the inventive process, the process for forming a mineral, food or pharmaceutical grade salt product comprises the steps of:
(a) loading or providing reactants necessary for making the mineral, food or pharmaceutical grade salt product in a reactor vessel;
(b) with optional mixing, adjusting the temperature of the reactants to a first set point temperature in the reactor vessel, wherein the first set point temperature is above about 25xc2x0 C. when operating the process at about 1 atmosphere pressure;
(c) with optional mixing, adding a fluid to the reactants of step (b) at a rate and in an amount sufficient to initiate reaction of all or nearly all of the reactants to form a first mixture; and
(d) with optional mixing, adjusting the temperature of the first mixture to a second set point temperature for a time sufficient to evaporate substantially all of the fluid to yield the mineral, food or pharmaceutical grade salt product having a desired moisture content. According to another embodiment, the xe2x80x9cmixingxe2x80x9d in any of steps (b), (c) and/or (d) may be intermittent or continuous. Further, according to still another embodiment, the desired moisture level is dictated by the product specification and is typically less than about 10-12%, preferably less than about 7%, more preferably less than about 6%, even more preferably from about 1 to about 6% and most preferably from about 1% to about 4%.